I would be interested to hear stories about whether it changes as demographics changes. If there is a declining birth rate, does culture move toward the middle

I would be interested to hear stories about whether it changes as demographics changes. If there is a declining birth rate, does culture move toward the middle aged? I would like to think so, but I've read that Japan is still a youth culture despite aging population. Maybe the opposite is true, as the article implies. When mortality is high and there are fewer old people they acquire value through scarcity.